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ChemComm
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DOI: 10.1039/C6CC00635C
COMMUNICATION
Journal Name
Kobayashi, T. Kawashima, J. Am. Chem. Soc. 2009, 131, 14192; (d) T.
Ureshino, T. Yoshida, Y. Kuninobu, K. Takai, J. Am. Chem. Soc., 2010,
132, 14324; (e) Y. Liang, W. Z. Geng, J. N. Wei, Z. F. Xi, Angew. Chem.
Int. Ed., 2012, 51, 1934; (f) K. B. Ouyang, Y. Liang, Z. F. Xi, Org. Lett.,
2012, 14, 4572; (g) Q. W. Zhang, K. An, L. C. Liu, Y. Yue, W. He,
Angew. Chem. Int. Ed. 2015, 54, 6918.
10 1a was prepared from 1-bromo-2-iodobenzene by 3 steps in an
overall 90% yield. See Supporting Information for details.
11 (a) K. Kalyanasundaram, Coord. Chem. Rev., 1982, 46, 159; (b) A.
Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser, A. von
Zelewsky, Coord. Chem. Rev., 1988, 84, 85.
12 The reaction was conducted in an oven-dried 10 mL borosilicate vial
equipped with a magnetic stir bar and rubber septum under
irradiation by a 23W household compact fluorescent lamp (CFL) at a
distance of ~5 cm. The typical household light bulb (Philips Tornado
23W) is available at Walmart Stores which has a wide spectral
window (~400 to 700 nm). The excitation (λmax= 452nm) of Ru(bpy)3
just fall within the scope.
Scheme 4. Functionalization of benzosiloline 3a.
2+
reacted as allylsilane with Selectfluor® to provide fluor-substituted
phenylsilanol 11 in 70% yield.25
13 The product, in which the R group falls on the same side as the
forming C-C bond, is assigned to have a Z configuration.
14 The ring-opening by-product was obtained in 31% yield. See
Supporting Information for details.
In summary, we have described an efficient approach to
synthesize benzosiloline by
a visible light-promoted radical
cyclization of silicon-tethered alkyl iodide and phenyl alkyne. The
nature of the terminal substituent of alkyne showed a great impact
on the configurational control of the exo-cyclic alkene in
benzosiloline. Rationalization based on a radical mechanism was
proposed to explain this contrasting stereochemcial outcome. The
synthetic values of benzosiloline was also demonstrated by
transformations into other useful synthons. Further applications of
this method are underway.
15 No obvious improvement of the E/Z ratio was observed using DMSO
as additive.
16 J. W. Wilt, F. G. Belmonte, P. A. Zieske, J. Am. Chem. Soc., 1983, 105
5665.
,
17 (a) L. A. Singer, N. P. Kong, J. Am. Chem. Soc., 1966, 88, 5213; (b) R.
W. Fessenden, J. Chem. Phys. 1967, 71, 74; (c) J. A. Kampmeier, M. S.
Lui, S. Soloway, D. K. Wedegaetner, J. Am. Chem. Soc., 1971, 93
3809; (d) D. P. Curran, D. Kim, Tetrahedron 1991, 32, 6171; (e) C.
,
Galli, P. Gentili, A. Guarnieri, Z. Rappoport, J. Org. Chem. 1996, 61
8878.
,
We are grateful for financial support from the NSFC (21321061,
21290180), the NCET (12SCU-NCET-12-03), and the Sichuan
University 985 project.
18 See Supporting Information for more details of computational
investigations.
19 Previous investigations have reported that the rate constant of H-
abstraction of a vinyl radical from n-Bu3SnH is ca. 108 M-1 s-1 at 30 °C.
Thus, if two bent isomers endowed with an inversion barrier greater
than 6-7 kcal/mol, the stereochemistry should be dependent on the
relative stability of Z and E-isomers. While the inversion barrier of
5.2 kcal/mol in our case is slightly lower than 6.0 kcal/mol, the
stereochemistry might be still dictated by the relative populations of
7-alkyl-Z and 7-alkyl-E if considering that other factors such
hydrogen donor, solvent and temperature, etc. would also affect the
stereochemical control. For references, see: (a) D. P. Curran,
Synthesis 1988, 417; (b) C. Galli, A. Guarnieri, H. Koch, P. Mencarelli,
Z. Rappoport, J. Org. Chem. 1997, 62, 4072.
Notes and references
1
For recent reviews, see: (a) S. G. Zhang, Z. F. Xi, Prog. Chem., 2009,
21, 1487; (b) W. X. Zhang, S. G. Zhang, Z. F. Xi, Acc. Chem. Res., 2011,
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3
For a latest review, see: A. Čusak, Chem. Eur. J., 2012, 18, 5800.
For selected examples, see: (a) N. P. Mulholland, G. Pattenden,
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4
For recent examples, see: (a) K. S. Bloome, R. L. McMahen, E. J.
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20 (a) J. A. Kampmeier, C. Chen, J. Am. Chem. Soc. 1965, 87, 2608; (b) B.
Giese, Angew. Chem. Int. Ed., 1983, 22, 753.
21 Using the bulkier hydrogen donor Ph2SiH2 in cyclization of 1l
unexpectedly gave an E/Z ratio of 78:22 comparable with 80:20
obtained using smaller PhSiH3. A possible reason might be that
increasing the bulkiness of hydrogen donor would increase the steric
repulsion proportionately in both path A and B. Other important
factors, which we currently cannot clarify, probably also play crucial
roles for the stereochemical control.
22 The syn-stereochemistry was assigned based on the results from
previous studies, which provided structurally similar products to
ours. See Supporting Information for details. For related references,
see: (a) K. H. Kim, H. S. Lee, S. H. Kim, K. Y. Lee, J.-E. Lee, J. N. Kim,
Bull. Korean Chem. Soc. 2009, 30, 1012; (b) H.-J. Gais, L. R. Reddy, G.
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Bandini, P. G. Cozzi, P. M., A. Umani-Ronchi, Angew. Chem. Int. Ed.
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MacMillan, Chem. Rev., 2013, 113, 5322; (b) D. M. Schultz, T. P.
Yoon, Science, 2014, 343, 985; For selected examples, see: (c) D. A.
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D’Amato, J. M. R. Narayanam, C. R. J. Stephenson, Nat. Chem., 2012,
4, 854; (g) Ł. Woźniak, J. J. Murphy, P. Melchiorre, J. Am. Chem. Soc.,
2015, 137, 5678.
7
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For a latest advance, see: Z. J. Liu, X. L. Lin, N. Yang, Z. S. Su, C. W.
Hu, P. H. Xiao, Y. Y. He, Z. L. Song, J. Am. Soc. Chem. 2016, 138, 1877.
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25 M. Tredwell, K. Tenza, M. C. Pacheco, V. Gouverneur, Org. Lett.,
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4 | J. Name., 2012, 00, 1-3
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